Is it possible to configure Reqnroll to run using STA (Single-Threaded Apartment)?

[Pressacco]

Dear Reqnroll community.

I am currently exploring the idea of combining Reqnroll with ViewModel level testing of a C# WPF application.

The Problem

Approach 1

Apparently you can configure MS Test to run in STA mode by simply:

using System.Threading;
using Microsoft.VisualStudio.TestTools.UnitTesting;

[TestClass]
public class TestInitialization
{
    [AssemblyInitialize]
    public static void AssemblyInit(TestContext context)
    {
        // Set the main thread to Single-Threaded Apartment
        Thread.CurrentThread.SetApartmentState(ApartmentState.STA);
    }
}

Problem:

• Unfortunately this does not work with Reqnroll, because AssemblyInitialize can only be referenced once & Reqnroll uses this attribute in the generated Reqnroll code behind.

Approach 2

The following code compiles & runs as expected:

        // https://www.meziantou.net/mstest-v2-customize-test-execution.htm
        public class StaTestClassAttribute : TestClassAttribute
	{
		public override TestMethodAttribute GetTestMethodAttribute(TestMethodAttribute testMethodAttribute)
		{
			if (testMethodAttribute is StaTestMethodAttribute)
				return testMethodAttribute;

			return new StaTestMethodAttribute(base.GetTestMethodAttribute(testMethodAttribute));
		}
	}

        [StaTestClass]
	public class UnitTestClass
	{
		[TestMethod]
		public void UnitTestExample()
		{
                        // Use NSubstitute to create a mock window
			var mainWindow = Substitute.For<Window>();

                        // pass in the Window dependency
                        var  viewModel = new DashboardViewModel(mainWindow);

                       // act
                       
                       // assert
                }
       }

Problem:

• When this line Substitute.For<Window>() is called from a Reqnroll step, .NET Core 8 throws an exception:
  • InvalidOperationException The calling thread must be STA, because many UI components require this.

Question

Is there an easy way to configure Reqnroll to run in STA mode? Any guidance you can provide would be appreciated.

Context

• .NET Core 6
  • WPF application
• MS Test 3.6.0
• Reqnroll 2.1.0

Related Discussions

• WPF STA Testing in ReqnRoll #133

---

It would be nice if the view model only referenced other view models (i.e. had no concept of a WPF Window), but let's assume that I do not have control over this implementation detail.

[gasparnagy]

Maybe you could do it with an in-project Reqnroll plugin. You would only need to add this to your project (not tested):

using Reqnroll.BoDi;
using Reqnroll.Infrastructure;
using Reqnroll.Plugins;
using Reqnroll.UnitTestProvider;

[assembly: RuntimePlugin(typeof(STAPlugin ))]

namespace YourNamespace;

public class STAPlugin : IRuntimePlugin
{
    public void Initialize(RuntimePluginEvents runtimePluginEvents, RuntimePluginParameters runtimePluginParameters, UnitTestProviderConfiguration unitTestProviderConfiguration)
    {
        // this code is called from the assembly initialize, so doing it simply here could work:
        Thread.CurrentThread.SetApartmentState(ApartmentState.STA);

        runtimePluginEvents.CustomizeGlobalDependencies += (sender, args) =>
        {
            // if the above does not work, you can also try it here
        };
    }
}

[Pressacco]

Unfortunately calling Thread.CurrentThread.SetApartmentState(ApartmentState.STA); anywhere within IRuntimePlugin results in an exception being thrown:

InvalidOperationException: Failed to set the specified COM apartment state. Current apartment state 'MTA'.

Ideally in MVVM, the ViewModel shouldn't know about a Window. I am going to try to refactor my code in order to remove the Window references.

Thank you @gasparnagy for taking the time to respond to my question.